DATA COMM & COMPUTER NETWORKING

Data Communications..  are the exchange of data between two devices via some  form of transmission medium such as a wire cable.

Telecommunication defined..  includes telephony, telegraphy, and television, means communication at a distance.  “tele” is Greek for “far”.

Four Fundamental Characteristics of the Effectiveness of Data Comm.  Delivery. The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user.  Accuracy. The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable.

Four Fundamental Characteristics (continued..)  Timeliness. The system must deliver data in a timely manner. Data delivered late are useless. In the case of video and audio, timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay. This kind of delivery is called real-time transmission.

Four Fundamental Characteristics (continued..)  Jitter. Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets.

Five Components of Data Communications  Message. The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video.  Sender. The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on.

Five Components of Data Communications (continued..)  Receiver. The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on.  Transmission medium. The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.

Five Components of Data Communications (continued..)  Protocol. A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese.

Data Representation  Text  Numbers  Images  Audio &  Video

Data Representation (continued..)  Text. In data communications, text is represented as a bit pattern, a sequence of bits (Os or Is).  Different sets of bit patterns have been designed to represent text symbols.  Each set is called a code, and the process of representing symbols is called coding.

Data Representation (continued..)  Numbers are also represented by bit patterns. However, a code such as ASCII is not used to represent numbers; the number is directly converted to a binary number to simplify mathematical operations.

Data Representation (continued..)  Images are also represented by bit patterns. In its simplest form, an image is composed of a matrix of pixels (picture elements), where each pixel is a small dot. The size of the pixel depends on the resolution.

Data Representation (continued..)  Audio refers to the recording or broadcasting of sound or music.  Audio is by nature different from text, numbers, or images.  It is continuous, not discrete.

Data Representation (continued..)  Video refers to the recording or broadcasting of a picture or movie.  Video can either be produced as a continuous entity (e.g., by a TV camera), or it can be a combination of images, each a discrete entity, arranged to convey the idea of motion.

Data Flow

Data Flow >> Simplex  In simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive.  Keyboards and traditional monitors are examples of simplex devices. The keyboard can only introduce input; the monitor can only accept output. The simplex mode can use the entire capacity of the channel to send data in one direction.

Data Flow >> Half-Duplex  In half-duplex mode, each station can both transmit and receive, but not at the same time.  When one device is sending, the other can only receive, and vice versa.  The half-duplex mode is like a one-lane road with traffic allowed in both directions.

Data Flow >> Half-Duplex (continued..)

 Walkie-talkies and CB (citizens band) radios are both half-duplex systems.  The half-duplex mode is used in cases where there is no need for communication in both directions at the same time; the entire capacity of the channel can be utilized for each direction.

Data Flow >> Full-Duplex  In full-duplex mode(also called duplex), both stations can transmit and receive simultaneously.  The full-duplex mode is like a two-way street with traffic flowing in both directions at the same time.  In full-duplex mode, signals going in one direction share the capacity of the link: with signals going in the other direction.  The full-duplex mode is used when communication in both directions is required all the time. The capacity of the channel, however, must be divided between the two directions.

Thank you and dismiss!